In today's radio communications networks a number of different technologies are used, such as Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. A radio communications network comprises radio base stations providing radio coverage over at least one respective geographical area forming a cell. The cell definition may also incorporate frequency bands used for transmissions, which means that two different cells may cover the same geographical area but using different frequency bands. User equipments (UE) are served in the cells by the respective radio base station and are communicating with respective radio base station. The UEs transmit data over an air or radio interface to the radio base stations in uplink (UL) transmissions and the radio base stations transmit data over an air or radio interface to the UEs in downlink (DL) transmissions.
Above mentioned existing 3rd Generation Partnership Project (3GPP) systems, including Second Generation (2G)/Third Generation (3G) systems and the newly emerging System Architecture Evolution (SAE)/LTE system, support the possibility to trace a particular user of a user equipment and/or a UE throughout its lifetime in the radio communications network, where the users for tracing may be selected based on: user identity, e.g. International Mobile Subscriber Identity (IMSI) based trace; terminal identity e.g. International Mobile Equipment Identity (IMEI) based trace; or based on location e.g. cell trace. During tracing all network activities related to the particular UE may be logged and later delivered to a central management entity, also called network management node, for evaluation. Logged network activities comprise signaling messages sent/received either on the radio interface or on network node interfaces. Some typical use cases of the result of such a tracing are to e.g. troubleshoot problematic connections to a particular user, e.g. in response to complaints from the particular user of the UE, or to monitor generic network performance and to perform root cause analysis to identify network problems.
According to a legacy trace concept, the trace target, e.g. a UE, and the trace configuration are specified by the network management node, which sends the configuration to the involved network nodes. In the trace configuration there is possibility to specify the interface(s) from which trace logs are to be collected, as well as, the level of trace information details, e.g., all message elements logged or only most relevant ones.
In current 3GPP systems there are two ways to activate a tracing, either via “signaling based activation” or “management based activation”. In “signaling based activation” the trigger for tracing a particular UE is propagated piggy-backed on the regular UE-specific signaling messages sent between the network nodes which the user data flow of the particular UE passes through. Initially the management system configures the particular UE for tracing in the Home Subscriber System (HSS) or in core network nodes e.g. Mobility Management Entity (MME), Serving General Packet Radio Services (GPRS) Support Node (SGSN) based on the IMSI of the user/subscriber or IMEI of the UE. As soon as the UE with the given IMSI or a UE with the IMEI appears in the system and the HSS is interrogated for user information, e.g., security credentials at user attach, a trigger for activating the tracing may be propagated to related network nodes via the invoked signaling flow. In “management based activation” the trigger for activating the tracing is not propagated to other nodes. The management system configures selected network nodes to trace a particular UE or set of UEs. When a new user or UE appears at the given network node, it evaluates the selection criteria and starts trace recording in case the criteria is satisfied.
More recently, 3GPP has started to work with the concept of “UE based network performance measurements”, also called, Minimization of Drive Test (MDT) measurements, where the objective is to utilize the network measurements done by the UE for network performance monitoring and optimization purposes. For the management of such UE measurements 3GPP has selected to use the trace concept, which means that the network management node may configure and collect such measurements by using the trace methods. 3GPP has also defined a number of requirements on selection options that shall be defined in the standard and shall be available for the network operator to specify which UEs shall take part in a measurement campaign e.g., selected based on IMSI and/or IMEI, cell, device capabilities and/or combinations of these. There are two types of MDT measurement modes defined, the so called immediate MDT measurements, which are performed when the UE is in a connected mode, and the so called logged MDT measurements, which are performed when the UE is in an idle mode. Immediate MDT measurements are associated with immediate reporting, i.e., the UE sends measurement reports as it collects them and no temporary storage in the UE is performed. Logged MDT measurements are associated with logged reporting when the UE collects and logs a number of measurement reports and sends them to the radio communications network in a bundle the next time when it enters connected mode.
An important aspect of MDT measurements is whether location information, i.e. position, can be associated with the measurements. Obviously, when position is available there is room for more advanced network optimization and performance observation use cases. It has been accepted as a requirement for MDT to support the reporting of UE position as a complement to MDT measurement data in order to enable network optimization use cases such as localizing coverage and/or capacity problems and to use MDT measurements as a replacement of regular drive tests in accordance with the original intentions of MDT. It has also been agreed that the UE may include any positioning information in the MDT measurement reports that it may have, for instance GPS coordinates or Radio Frequency (RF) fingerprints. On the other hand, 3GPP systems already support network based UE positioning methods, which are available both in Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) and in Evolved-UTRAN (E-UTRAN). The positioning methods may broadly be classified as: (1) UE based positioning; and (2) UE assisted and/or network based positioning. In the first case the positioning may be calculated by the UE itself with or without assistance from the positioning node. In case of UE assisted and/or network based positioning, the position is calculated by the network, e.g. the positioning node, typically utilizing UE measurements as well. The positioning node performing the positioning calculation in the network may be a Serving Mobile Location Centre (SMLC) or Enhanced-SMLC (E-SMLC) in case of E-UTRAN.
In e.g. the current LTE system, the UE and network measurements for positioning purposes go transparently over the radio network and thereby there is no possibility to collect these measurements and send them to the Operation and Maintenance (OAM) system for processing, i.e., for calculation of UE position. Thus, an OAM node is not able to calculate position of a UE for MDT measurements. Using the network based positioning architecture, e.g. E-SMLC based positioning, would have its limitation in terms of signaling and processing scalability. The E-SMLC based positioning has been designed to support location based services, i.e., occasional and one time positioning. In case of MDT measurements the positioning needs to be executed for a large number of UEs, potentially in the entire network, and continuously with second level periodicity, to which the E-SMLC based solution would not scale.